This book is about some topical philosophical and methodological prob lems that arise in the study of behavior and mind, as well as in the treatment of behavioral and mental disorders. It deals with such questions as 'What is behavior a manifestation of?', 'What is mind, and how is it related to matter?', 'Which are the positive legacies, if any, of the major psychological schools?', 'How can behavior and mind best be studied?', and 'Which are the most effective ways of modifying behavioral and mental processes?' These questions and their kin cannot be avoided in the long run because they fuel the daily search for better hypotheses, experimental designs, techniques, and treatments. They also occur in the critical examination of data and theories, as well as methods for the treatment of behavioral and mental disorders. All students of human or animal, normal or abnormal behavior and mind, whether their main concern is basic or applied, theoretical or em pirical, admit more or less tacitly to a large number of general philosophi cal and methodological principles.